-- * Constructing normal syntax
mkCoreLet, mkCoreLets,
mkCoreApp, mkCoreApps, mkCoreConApps,
- mkCoreLams,
+ mkCoreLams, mkWildCase, mkIfThenElse,
-- * Constructing boxed literals
mkWordExpr, mkWordExprWord,
import TysWiredIn
import PrelNames
-import MkId ( seqId )
import Type
import TypeRep
import FastString
import UniqSupply
+import Unique ( mkBuiltinUnique )
import BasicTypes
import Util ( notNull, zipEqual )
import Panic
-----------
mk_val_app :: CoreExpr -> CoreExpr -> Type -> Type -> CoreExpr
mk_val_app (Var f `App` Type ty1 `App` Type _ `App` arg1) arg2 _ res_ty
- | f == seqId -- Note [Desugaring seq (1), (2)]
+ | f `hasKey` seqIdKey -- Note [Desugaring seq (1), (2)]
= Case arg1 case_bndr res_ty [(DEFAULT,[],arg2)]
where
case_bndr = case arg1 of
Var v1 | isLocalId v1 -> v1 -- Note [Desugaring seq (2) and (3)]
- _ -> mkWildId ty1
+ _ -> mkWildBinder ty1
mk_val_app fun arg arg_ty _ -- See Note [CoreSyn let/app invariant]
| not (needsCaseBinding arg_ty arg)
= App fun arg -- The vastly common case
mk_val_app fun arg arg_ty res_ty
- = Case arg (mkWildId arg_ty) res_ty [(DEFAULT,[],App fun (Var arg_id))]
+ = Case arg arg_id res_ty [(DEFAULT,[],App fun (Var arg_id))]
where
- arg_id = mkWildId arg_ty -- Lots of shadowing, but it doesn't matter,
- -- because 'fun ' should not have a free wild-id
+ arg_id = mkWildBinder arg_ty
+ -- Lots of shadowing, but it doesn't matter,
+ -- because 'fun ' should not have a free wild-id
+ --
+ -- This is Dangerous. But this is the only place we play this
+ -- game, mk_val_app returns an expression that does not have
+ -- have a free wild-id. So the only thing that can go wrong
+ -- is if you take apart this case expression, and pass a
+ -- fragmet of it as the fun part of a 'mk_val_app'.
+
+
+-- | Make a /wildcard binder/. This is typically used when you need a binder
+-- that you expect to use only at a *binding* site. Do not use it at
+-- occurrence sites because it has a single, fixed unique, and it's very
+-- easy to get into difficulties with shadowing. That's why it is used so little.
+mkWildBinder :: Type -> Id
+mkWildBinder ty = mkSysLocal (fsLit "wild") (mkBuiltinUnique 1) ty
+
+mkWildCase :: CoreExpr -> Type -> Type -> [CoreAlt] -> CoreExpr
+-- Make a case expression whose case binder is unused
+-- The alts should not have any occurrences of WildId
+mkWildCase scrut scrut_ty res_ty alts
+ = Case scrut (mkWildBinder scrut_ty) res_ty alts
+
+mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
+mkIfThenElse guard then_expr else_expr
+-- Not going to be refining, so okay to take the type of the "then" clause
+ = mkWildCase guard boolTy (exprType then_expr)
+ [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
+ (DataAlt trueDataCon, [], then_expr) ]
\end{code}
Note [Desugaring seq (1)] cf Trac #1031